Classifications

• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B6/00—Heating by electric, magnetic or electromagnetic fields
  • H05B6/02—Induction heating
  • H05B6/10—Induction heating apparatus, other than furnaces, for specific applications
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K3/00—Tools, devices, or special appurtenances for soldering, e.g. brazing, or unsoldering, not specially adapted for particular methods
  • B23K3/04—Heating appliances
  • B23K3/047—Heating appliances electric
  • B23K3/0475—Heating appliances electric using induction effects, e.g. Kelvin or skin effects
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K9/00—Arc welding or cutting
  • B23K9/235—Preliminary treatment
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B3/00—Ohmic-resistance heating
  • H05B3/10—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor
  • H05B3/12—Heating elements characterised by the composition or nature of the materials or by the arrangement of the conductor characterised by the composition or nature of the conductive material

Definitions

• Curie temperature heaters and more particularly to auto ⁇ regulating Curie temperature heaters in which control of zones of heating and at least partial control of resistance is provided by slotting the outer conductor of the device which technique may also be employed to lend bendability to a restricted region as well as flexi ⁇ bility to the entire heater or specific regions thereof.
• an autoregulating electric heater having a laminated structure; one lamina of which has high magnetic permeability and high resistance and another lamina of which is non-magnetic and has a low resistance (such as copper) in ele ⁇ trica contact and, therefore, thermal contact with the first lamina.
• This structure is adapted to be connected across a constant current, a.c. source such that the layers are in a sense in parallel across the source. Due to skin effect, the current is initially confined to the high magnetic permeability, high resistance layer
• the current source employed in the aforesaid patent is typically a high frequency source, for instance, 8 to 20 MHz to insure that the current is confined to the thin, high resistivity, magnetic layer until the Curie temperature of the magnetic material is attained.
• a high frequency source for instance, 8 to 20 MHz to insure that the current is confined to the thin, high resistivity, magnetic layer until the Curie temperature of the magnetic material is attained.
• the maximum regulation is achieved when the thickness of the magnetic layer is of the order of one skin depth at the frequency of operation. Under these circumstances, the maximum change in effective resistance of the structure is achieved at or about the Curie temper ⁇ ature. This fact can be demonstrated by reference to the equation for the skin depth in a monolithic, i.e., non-laminar magnetic structure: S.D.
• Difficulty may arise in such devices when the Curie temperature is achieved due to spread of the current and/or magnetic, flux into adjacent regions outside of the device, particularly if the device is located close to sensitive electrical components.
• the magnetic field in a simple, single layer, i.e., monolithic structure falls off as e ⁇ x so that at three skin depths, the field is 4.9% of maximum, at five skin depths, it is 0.67%, and at ten skin depths, the field is .005% of maximum.
• thicknesses of three skin depths are satisfactory although at least five are preferred and in. some cases ten or more may be required with some highly sensitive devices in the vicinity of large heating currents.
• the devices of the patent and aforesaid application are operative for their intended purposes when connected to a suitable supply, but a drawback is the cost of the high frequency power supply.
• the frequency of the source is preferably maintained quite high, for instance, in the megahertz region, to be able to employ copper or other non-magnetic material having reasonable thicknesses.
• a relatively low frequency constant current source may be employed as a result of fabricating the normally non-magnetic, low resistivity layer from a high permeability, high Curie temperature material.
• the device comprises a high permeability, high resistivity first layer adjacent the current return path and a high permeability impart preferably low resistivity second layer remote from the return path; the second layer having a higher Curie temperature than the first-mentioned layer.
• high magnetic permeability refers to materials having permeabilities greater than paramagnetic materials, i.e., ferromagnetic materials, although permeabilities of 100 or more are preferred for most applications.
• the theory of operation underlying the invention of the aforesaid application filed on September 30, 1982, is that by using a high permeability, high Curie tempera ⁇ ture material as the iow resistivity layer, the skin depth of the current in this second layer is such as to confine the current to quite thin layer . even at low frequencies thereby essentially insulating the outer surfaces electrically and magnetically but not thermally with a low resistivity layer of manageable.thickness.
• the second layer is preferably formed of a low resistivity material, but this is not essential.
• An example of a device employing two high mu laminae utilized a layer of Alloy 42 having a resistivity of about 70-80 micro-ohms-cm, a permeability about 200, and a Curie temperature of approximately 300° centigrade.
• a second layer is formed of carbon steel having a resis ⁇ tivity of about 10 micro-ohms-cm, a permeability of 1000, and a Curie temperature of about 760° centigrade.
• the skin depths, using a 60 Hz supply are .1" for Alloy 42 and .025" for carbon steel.
• An example of a practical 60 Hz heater based on the above may employ a coaxial heater consisting of a .25" diameter cylindrical or tubular copper conductor (the "return” conductor) , a thin layer (perhaps .002 in thickness) of insulation, followed by the temperature sensitive magnetic alloy having a perme- ability of 400 and a thickness of 0.1", and finally an outear jacket of steel having a permeability of 1000 and a thaekness. of 0.1".
• the overall heater diameter would be ⁇ 65". If the heater is used in a situation requiring 5 watts per foot of heater length for, for instance, protection of a liquid against freezing, the total length of the heater is 1000 feet, the resistance of the heater will be 1.96 ohms.
• the current will be 50 amperes, and the voltage at the generator end will be 140 volts at temperatures somewhat below the Curie temperature of the temperature sensitive magnetic alloy on the inside of the outer pipe. If there were substantial changes in the electrical resistance due to variations of the thermal load, the required voltage must vary in order to maintain constant current.
• Such a supply provides current at costs considerably less than a constant current supply at 8-20 MHz.
• the power regulation ratios (AR) in such a device are not as high as with the device of the patent with a resistivity difference of about 10:1, but the AR difference may be reduced by using materials of -7- higher and lower resistivities for the low Curie tempera ⁇ ture and high Curie temperature materials, respectively. Also, a high mu, relatively low resistivity material such as iron or low carbon steel may be employed to further increase the power regulation ratio.
• the objects of the invention are achieved by providing a region of high conductivity at the interface of the two members having high permeability as set forth in the Krumme application, S.N. 430,317, filed September 30, 1982.
• the material in the interface region may be copper, for instance, or other highly conductive material.
• the material may appear as a separate layer, a sandwich of magnetic, non-magnetic and magnetic material or may be bonded to the high and/or low Curie temperature, ferro ⁇ magnetic layers at the interface to provide a low resistivity, interface region.
• Typical thicknesses of the sandwich construction at 1 KHz are 0.03" for both the low and high Curie tempera ⁇ ture ferromagnetic materials, respectively, and .010" for the copper layer.
• a low frequency is meant a source in the range of 50 Hz to 10,000 Hz although 50 Hz-8000 Hz is fully adequate.
• a flat ' , elongated return conductor is covered with insulation,* a flat strip -9- of high mu, that is, ferromagnetic or other, material exhibiting ferromagnetic properties is disposed along one of the flat elongated surfaces of the return conductor.
• the structure may then be covered by a conductive material having transverse, spaced slots formed in the surface remote from the high mu material.
• the structure is flexible relative to prior structures because of the slots and because the high mu material is a thin layer lying only along one major surface; the surface opposite the slots.
• Resistance of the device is greatly increased relative to prior devices of this type because the cross-sectional area of both the high mu material and the outer layer is greatly decreased and thus current density is increased, raising resistance.
• the cross-sectional area of the outer layer is raised because no current flows in the region of the transverse slots; it is confined by the slots to the region of the high mu material, particularly below Curie temperature. Regions of and degree of heating may be controlled by various methods. First, flat high mu members of different Curie temperatures may be disposed at different locations along the device, thus establishing different autoregulating temperatures at these different zones.
• the slotted surface may be unslotted in some regions permitting the current to be at least partially diverted from the ferromagnetic material in such regions thereby preventing the device from reaching Curie temperature in such region or simply decreasing resistance in that region. Partial reduction in slotting (shorter slots) may be employed to divert sufficient current to increase the time to reach autoregulating temperatures.
• the heater may be made such that it depends for auto- regulation on simply increasing the cross-sectional area -10- of the ferromagnetic material in which current flows. This approach may be achieved by employing a high mu material of a thickness of three or more (depending upon the type of heater) skin depths at Curie temperature.
• a heater in accordance with the aforesaid patent may be achieved by having a ferromagnetic material of 1 to 1.8 skin depth below Curie temperature and an outer layer of appropriate thickness.
• the ferromagnetic material may be one lamina of a high mu and copper laminate.
• the outer layer can be stainless steel or other material of high stain resistance and/or good thermal conductivity.
• the slots in the surface of the outer conductor may also be employed to provide appropriate bend areas where a strap must go around sharp corners.
• Fig. 1 is a perspective view of one form of heater in accordance with the present invention.
• Fig. 2 is a cross-sectional view taken along section line 2-2 of Fig. 1.
• Fig. 3 is a view in cross-section of a modification of the heater of Fig. 2.
• Fig. 4 is a view in cross-section of a multitemperature heater.
• Fig. 5 is a perspective view of a heater employing various arrays of slots to define different heating patterns.
• Fig. 6 is a view in cross-section taken along section line 6-6 of Fig. 5.
• Fig. 7 is a perspective view illustrating the use of a slot to enhance bendability of a heater in accordance with the present invention.
• Fig. 8 is a view in perspective of another embodiment of the present invention. -1 1 -
• a current return 5 path is provided by an inner flat elongated conductor 2 usually of copper.
• the conductor 2 is surrounded by an insulating layer 4 and in one embodiment of the invention a layer 6 of ferromagnetic material is arrayed along the bottom of the structure.
• An outer covering 10 8 is also provided to shield the structure, the material of the outer covering, to some extent, being determined by the intended use of the device, as will be discussed subsequently.
• the outer covering 8 in accordance with one aspect 15. of the invention is provided with a plurality of closely spaced transverse slots 10 which in the form illustrated extend across the top of the device as illustrated in figures 1 and 2 and down both side ' s thereof leaving a continuous web 12 of material along the bottom of the 20 device juxtaposed to the ferromagnetic layer 6.
• the current when applied, can flow only in the bottom region, as viewed in Figures 1 and 2, of the outer layer 8. Below Curie temperature, the current is primarily confined to the layer 6 of ferromagnetic 5 material, as the temperature of the heater, and more particularly of the layer 6, approaches Curie temperature. The current in layer 6 spreads and the resistance of the heater drops.
• the heater of Figure 2 may operate in one of two pos- 0 sible modes depending upon the thickness of the layer 6. If the layer 6 is at least five skin depths thick above Curie temperature, then virtually all of the current remains in the layer 6 but is not essentially confined to a skin depth of 1 to 1.8 below Curie* temperature. 5 The result is a decrease in resistance due to a material change in current density. Specifically, if the mu of -12- the ferromagnetic material falls from 400 below Curie temperature to 1 above Curie temperature, then skin depth changes by a factor of 20 (the square root of 400) . The . resistance, however, still remains relatively high since the typical resistivity of ferromagnetic material such
• Alloy 42 is about 75 x 10 ohm-cm while copper*'s is about 2 x 10 ⁇ ohm-cm.
• the ferromagnetic layer 6 would be 1 to 1.8 skin depth thick below Curie temperature. Upon approach of the temperature to Curie temperature the current would spread out of the layer 6 into the lower surface 12 of the outer shell 8. If the outer shell is copper, then a material change in resistance occurs, but the resistance is still materially greater than in the prior devices since current flows only in region 12; the slots 10 blocking flow in all other regions.
• the resistance characteristics of the outer layer become of less concern and various materials such as stainless steel, aluminum, etc., may be employed.
• FIG. 3 An outer layer of any desired material may also be employed with the device of Figure 3..
• a device is illustrated that is quite similar to that of Figure 2 and which operates as the device of the aforesaid patent.
• Reference numerals with primes in Fig. 3 designate parts that correspond to those of Figure 2.
• the only difference between the heater of the two figures resides in the fact that the layer 6 1 is one lamina of a laminated structure including a second layer 14 which may be copper.
• the second layer may be a ferromagnetic material in accordance with application Serial No. 430,317 or a second layer of ferromagnetic material in conjunction with a copper layer between the two ferromagnetic layers as taught by application Serial No. 445,862.
• Ferromagnetic layer (length) 6.2 inches
• the outer layer 8* is made from a width of material folded about the heater with its elongated edges 16 and 18 brought into virtually abutting engagement. If moisture sealing is required the gap between edges 16 and 18 may be filled with a suitable conductive or non-conductive sealing material.
• the heater comprises an outer layer 20 of conductive material and an inner or current return conductor 22/ surrounded by insulation 24. Lying between the lower surface of the insulating material 22 and the - - lower surface of layer 20, all as viewed in Figure 4, are three longitudinally extending and spaced strips 26, 28 and 30 of ferromagnetic materials. Each of the strips has a different Curie temperature and thus each strip defines a zone of a different temperature from each other zone or alternatively strips 26 and 30 can be the same with strips 28 defining a different tempera ⁇ ture.
• the strips 26, 28 and 30 may also be arranged side by side. Referring now specifically to Fig.
• the heater generally designated by the reference numeral 32, has various slots for controlling the rate of heating to Curie temperature.
• the rate of heating of any heater is determined by the " .relationship between the rate of application of power and the rate of dissipation of heat by all of the three modes of heat dissipation from a surface, convection, conduction, and radiation. Heating up to the Curie temperature is determined by the current density in the ferromagnetic layer.
• any current path that is not adjacent the ferromagnetic material reduces the current density therein and reduces the rate of heating.
• the slot 34 permits current to flow in at least a part of the right side, as viewed in Fig. 5, of the outer shell or layer of the heater. Thus, some current is diverted from the ferromagnetic material and the rate of heating to Curie temperature is reduced. Slots 36, 37 and 38 may divert enough current from the ferromagnetic layer so that the heater never achieves Curie temperature, thus establishing a cool or more precisely a cooler zone than adjacent the slot 34.
• Slots 40 and 42 define a central current flow region 44 which may be employed to further reduce current flow adjacent the ferromagnetic layer.
• ferromagnetic material may be disposed under the region 44 so that heating occurs in this region.
• ferromagnetic material may encircle the heater under the outer layer whereby heating occurs at all locations except where there are slots.
• FIG. 6 of the accompanying drawings a figure taken along section line 6-6 of Fig. 5.
• a return conductor 46 is surrounded by insulation 48, in turn surrounded by a ferromagnetic layer 50 with an outer conductive shell 52. As indicated above, heating occurs at all locations except where there are slots.
• the current return conductor and the outer conductor, ferromagnetic layer or copper substrate, depending on the type of heater employed are connected in series with one another across the current source. This is usually accomplished by applying the current to the center and other conductors at one end of the device and connecting these conductors together at the other end of the device.
• the slots provided according to the present invention may also be employed to permit a heater to bend about a sharp corner.
• Fig. 7 of the accompanying drawings there is illustrated a rectangular workpiece 54 that is to be heated by a heater 56.
• the heater 56 is provided with a slot 58 so that the heater may come across the top of the workpiece 54, bent over the upper right corner 60 of piece 54 and maintain contact with vertical surfaces 62, all as illustrated in Fig. 7.
• the heater is rendered readily bendable -16- by using a simple slot while maintaining the rest of it relatively rigid so that good contact is maintained between heater and workpiece at all locations.
• a heater employing a 45° slot to permit right angle folding of a strap.
• a region 64 of strap 66 is slotted on its upper sur ⁇ face as at 68 to provide heating along the lower surface.
• the lower surface is provided with a 45° slot that permits a right angle fold 70 of the strap.
• the upper and lower surface of the folded length 72 of the strap may be slotted to permit heating of the lower or upper surface, the strap being flexible enough to permit the lower surface length 72 to contact the same surface as region 64.
• the region 72 or even region 64 may be unslotted to provide heating along all surfaces of the heater with, of course, appropriately located -ferromagnetic material.
• the slots in region 72 could be arrayed along the upper rather than the lower surface of the strip, as viewed in Fig. 8, so that heating remains along the upper surface. It should be apparent that the fold 70 could be other than 90° by changing the slot on the lower surface from 45° to some other desired angle.
• a slot of 30° to the longi ⁇ tudinal axis produces a fold of 60° while a slot of 60° will produce a fold of 120°.
• slots 68 they have been shown in all figures as perpendicular to the longitudinal axis of the strap. These slots may also be angled to produce a helix rather than an annulus. The angle may be chosen to produce a desired pitch when the strap is to be wrapped around a pipe, for instance, to keep it from freezing. The pitch desir ⁇ ably prevents overlap of adjacent turns of the helix and in fact be great enough to define a permissible spacing between turns as determined by the internal temperature required in the pipe and the ambient temperature.- -17-

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• Engineering & Computer Science (AREA)
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• Health & Medical Sciences (AREA)
• Dermatology (AREA)
• General Health & Medical Sciences (AREA)
• Plasma & Fusion (AREA)
• Electromagnetism (AREA)
• Resistance Heating (AREA)
• General Induction Heating (AREA)
• Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
• Air-Conditioning For Vehicles (AREA)
• Surface Heating Bodies (AREA)
• Heat-Pump Type And Storage Water Heaters (AREA)
• Mechanical Treatment Of Semiconductor (AREA)
• Pressure Welding/Diffusion-Bonding (AREA)

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• 1984
  • 1984-03-06 US US06/586,711 patent/US4717814A/en not_active Expired - Lifetime
• 1985
  • 1985-03-05 AT AT85301500T patent/ATE78384T1/de not_active IP Right Cessation
  • 1985-03-05 EP EP85301500A patent/EP0158434B1/en not_active Expired - Lifetime
  • 1985-03-05 DE DE8585301500T patent/DE3586331T2/de not_active Expired - Lifetime
  • 1985-03-05 CA CA000475791A patent/CA1253187A/en not_active Expired
  • 1985-03-06 JP JP60501326A patent/JPS61501354A/ja active Granted
  • 1985-03-06 WO PCT/US1985/000364 patent/WO1985004068A1/en unknown

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